Receiving apparatus for radiofrequency navigation systems



W. J. OBRIEN RECEIVING APPARATUS FOR RADIO-FREQUENCY NAVIGATION SYSTEMS Original Filed Aug. 27, 1945 donau-Q7:

IN VEN TOR.

M m WU 0 n. J w M Patented Jan. 20, 1953 RECEIVING APPARATUS FOR RADIO- FREQUENCY NAVIGATION SYSTEMS William J. OBrien, London, England, assignor to The Decca Record Company, Limited, London, England, a corporation of Great Britain Original application August 27, 1945, Serial No.

612,997, now Patent No. 2,530,902, dated November 12, 1950. Divided and this application June 15, 1950, Serial No. 173,408

6 claims. (c1. 34a-105) My invention relates to radio frequency navigational aids for determining and indicating the geographical location of a mobile vehicle and has particular reference to a novel form of receiving apparatus for use with navigational systems of the multiple equiphase displacement type.

This application is a division of my copending application Serial No. 612,997, filed August 27, 1945, and entitled Receiving Apparatus for Radio Frequency Navigation Systems, now Patent No. 2,530,902. In my copending application Serial` No. 107,337, .led July 28, 1949, now Patent No. 2,530,903, and `entitled Navigation Systemy (a continuation-in-part of anV earlier application led August 27, 1945), I have disclosed a radio frequency navigational system which operates to establish two intersecting coordinate systems defined by contours of equal phase displacement between interfering radio frequency elds of unlike but related frequencies. I have also disclosed in my Patent No. 2,500,200, issued March 14, 1950, a receiving apparatus which may be used on the mobile vehicle to receive the transmissions from the navigational equipment and provide a continuous indication of the coordinate location of the vehicle In the receiving apparatus described therein, the separately received signals are converted to a frequency equal to the least common multiple of the two frequencies the relative phase of which it is desired to determine. One possible objection to this mode of operation lies in the rather large amount of equipment required to effect the necessary frequency conversions. Also the apparatus disclosed is inherently of a xed frequency type which, once installed, is suitable for use only on a single set of transmitting apparatus.

My rst aforementioned copending application contemplates extending the coverage of the navigational system over extremely large areas by employing a plurality of individual systems of the type disclosed in that application and arranged to overlap their respective useful areas so as to extend the geographical coverage of the system. The mobile receiver in order to take advantage of the extended range and accuracy of such a system must be equipped with receiving means which will permit the proper one of the individual navigational systems to be selected out of the system network.

Because of the limitations above noted, the present invention is directed to a receiving apparatus which is simpler in construction than that which has been heretofore disclosed and which is provided with tuneable means permitting a user of the system to select any one of a group of navigational systems forming a system network.

It is therefore an object of my invention to provide a mobile receiving apparatus for use with navigational systems of the character above referred to and which operates to determine the relative phase relations at a frequency no greater than a signal frequency transmitted by the transmitting apparatus.

It is a, stillfurther object .of my invention to provide an appaartus of the nature above Aset forth in which means is provided for tuning the receiving apparatus to allow users of the system to choose one coordinate system out of a plurality of such systems produced by the operation of the navigational system network.

It is an additional object of my invention to provide a receiving apparatus of the character set forth in the preceding paragraphs which operates on a. heterodyne principle permitting the use of heterodyne frequency amplifiers which may be so constructed as to provide a high gain and excellent phase stability.

Other objects and advantages of my invention will be apparent from a study of the following specification read in connection with the single figure of .the drawing comprising a block diagram illustrating a tuneable receiving apparatus which works into fixed heterodyne frequency amplifiers arranged to make a phase comparison between the received signals at frequencies lower than the lowest transmitted frequency.

Referring to the drawings, I have illustrated by diagrammatical means the apparatus employed in my invention to provide a mobile receiving apparatus suitable for use with radio frequency navigational systems of the character disclosed in my first aforementioned copending application.

The operating frequencies of the various portions of the apparatus have been indicated in the figure by frequency notations enclosed in parentheses. It will be appreciated that the frequencies specified are those corresponding tothe assumed transmission frequencies of80, and kilocycles and that other frequencies will be employed whenever the transmitting equipment is operated at frequencies other than those assumed. l

With respect to the apparatus mentionedA in the ensuing description, the amplifiers, detectors,

frequency converters, phase discriminators and phase indicators may be of any suitable type.

The apparatus which is illustrated in the drawing.'` includes: variable frequencyamplifiers 3|, 32 and 33 the inputs'of which are connected respectively through single-pole double-throw switches 34, 35 and 36 to a suitable receiving.;

antenna 31.

The output of the amplifiers 3|,` 32..and 33.7are.

respectively coupled as indicated at 38, 39 and 4D to mixing and detecting circuits'4l, 42 Yand 43.: Associated respectively with the amplifiers 3 l',V 32 and 33 are variable frequency amplifiers-44, 45-

and 46. These amplifiers are coupled to ,be excited from a harmonic generatorV 4'|` the output of which is coupled as indicated'at- 48-through a high pass filter 49 having a lower cut-oifrequency of the order of magnitude of 45 kilocycles.

The high frequency signals passed bythe filter' 49 are coupled as indicated at 50,.5| and 52 to thel input circuitsy respectively of the ampliiers 44;5 45 'and 46.

The# amplifiers 44, 45V and 46 are-preferably of `the-*regenerative type designed to `produce an outputsignal as closely approaching a sinusoidal wave form as possible. Ifdesired the `amplifiers maybe made'regenerative'to suenan extent as to ybeself-oscillating. Theoutput's of these am'- pliers are respectively coupled as indicated at 53," 54'fand 55to' the input circuits of the `detectors 4|, 42 andh 43 Within which circuits the signals of different frequency'are mixed and rectified-to 'produce output lfrequencies equal to the/'difference between .the two "inputfrequenci'esf- In'faecordance with: the assumed example lthe harmonic generator preferably operates at a fundamental frequency of 112/3 kilocycles with the amplifiers 44, 45 and 46 being tuned respectively to the eighth, sixth and ninth harmonics of the fundamental frequency of the harmonic generator. The amplifier 44 is, therefore, tuned to 931/3 kilocycles, the amplifier. 45 is tuned to 'I0 kilocycles and the amplifier 46 is tuned to 105 kilocycles. As a result the output frequencies ofthe detectors 4|, 42 and 43 are respectively 131/3 kilocycles, 10 kilocycles and l5 kilocycles.

The-,detectors are coupled as indicated at`56, 51-and 58`to heterodyne frequency amplifiers 59, 6D and 6| adjusted respectively to operateat fixed frequencies of 131/3, 10and 15 kilocycles. The 13 l@ kilocycle outputof the `heterodyne frequency amplifier 59 is coupled asindicated at 6I toan amplifier .and frequencyv trebler 62 operating to produce a40 kilocycle outputA signal. which .is applied as indicated at 63 to one input circuit of :afphase discriminator 64..- The lOkilocycle output of theheterodyne frequency amplier 6|) is divided as indicatedat65 land 66 4and one-half of. the output is applied .to the input offa 10 kilocycle. amplier and frequency quadrupler 61 operating to convert the 10 kilocycle-input into a 40 kilocycle output, which output is appliedias indicated at (i8 to .the Aother input Vcircuit of the phase discriminator 64... The output of the phase discrimnator y|54 is coup1ed, .asindicated .at l|59. to av .phase :angle gindicator 10 .serving to .indicate the relative phase.. relation between the` .two 40 kilocycle signals applied to the discrirninatorv 64.

The other half Vof the lO'kilcycleoutput'of the heterodyne frequency amplifier 60'is Vapplied as indicated at '66 to 'a'10kilocycleampliii'er and frequency trebler 1| 4operating tol convert'the 10 kilocycle input into a 30 kilocycle output." This output'4 is applied as indicated at |2`to oneinput circuitLA of a `30 kilocycle phase'discriminator `13;

The 15 kilocycle output of the heterodyne frequency amplifier 6| is coup1ed as indicated at '|4 to a 15 kilocycle amplifier and frequency doubler'15.serving to produceA an outputfrequency of 30 kilocycles which is coupled-as indicated at 'I6 to the other input circuit of the phase discriminator 13. The phase discriminator operates to. measurethephase relation between the two 30ki1ocycle.input signals and to indicate by means of a phase indicator coup1ed to the discrii'ninator 13 as indicated at 18 the result of the determination of the phase angle between the two input signals.

It is to be notedthat the result of the phase determination-which `is indicated on the indicators 10' and --is the relative phase between the two-pair of navigational signals 'as measured on the basis of a reference frequency equal to the least common multiple of the respective transmitted frequencies. This may be explained as follows:

Assumethat a phase advancement of four degrees occurs in the kilocycle signal with'no phase/shift occurring in the 60 kilocycle signal as, for example, through movement ofthe mobile receiver in -a circularpathat a xed distance from the 60 kilocycle transmitting antenna. Thefleast'common multiple reference frequency for the 60 and 80 kilocycle signals is'240 kilocycles or three times the 80 rkilocycle signal. Therefore, the phase shift .at the reference frequency of 240 kilocycles will be al phase advancementgof twelve-degreescr three'times the actual advancement of the'kSO kilocycle signal'. The mixingof 'the 80'and `-931=kilocycle signals'iin thede'tector circuit 4| produces an'advancement of four degrees in the-131/3- kilocycle signal passed to the Afrequency trebler 62. The result of the frequency conversion is to advance the phase of the resulting 40 kilocycle signal three times as much as the advancement of the 131A; kilocycle signal or a vnet advancement of 'twelve degrees. Therefore, the phase 'advancement of the 40 kilocycle signal :applied to the phase discriminator 64 by means of the coupling 63 is twelve degrees, whereas no shift occurs in the signal coupled asV indicated at 65 and 68. The indicated phase shift on the indicator 10 will accordingly be an advancement of twelve degrees.

Similarly-if the phase of Ithe 60 kilocycle signal received by the `amplier32 advances three degreeswhile the phase-of the kilocyc1e signal received by the-amplifierl 33 remains constant the `indicated phasei'shift at thevlowest common multipleffrequency of 180 "kilocycles Will be nine degrees. A three'degree advancement ofthe phase of-thef() kilocycle signal results in athree degree advancement of the phase of the 10 kilocycle signal which is passed tothe-frequency treblerf'H. The frequency-trebling effected by this Ycircuit producesV a phase advancement of nine Zdegrees in the 30 kilocycle output applied as indicated at '|2to one input of 'the phase discriminator 13.' The phase of the signal applied tothe other input of the phase discriminator 13 remainsfconstant. The net effect is an indicated phase'shift of ninefdegreesfin'the advaricingjdhi` rection of the 60 kilocycle 'signal with respect. to the 90'klocycle signal..

In accordance with the present .modification of the invention the'amplifiers 3|-33 and 44-46 and the harmonic 'generator'41 are tuneable so that they may be used to select transmissions from other -antennaeatfrequencies different from the 80,l 60aiid 90 kilocycle signals used' in the assumed example. To simplify the tuningof the system to other transmitters, the tuning controls for the amplifiers and harmonic generator will, by preference, be ganged on a single control.

Assuming that the new transmitters desired to be received `are operating on 88, 66 and 99 kilocycles respectively, the tuning control used would be advanced to tune the amplifiers 3l, 32 and 33 respectively to these frequencies. At the same time the frequency of the harmonic generator 41 would be raised to 12% kilocycles. The tuning change of the amplifiers 44, 45 and 46 would be to resonance with the eight, sixth and ninth harmonics of the 122/3 kilocycle fundamental as before; in other words, to frequencies of 1011/3, 76 and 114 kilocycles. The resulting heterodyne frequencies are, therefore, unchanged, being respectively 13%, 10 and 15 kilocycles.

In addition to the foregoing I prefer to provide a means for periodically checking the operation of the system to detect any spurious and unwanted phase shifts which may creep into the various circuits. For this reason I employ also a reference oscillator 19 normally operating on a kilocycle fundamental signal to produce an output which is rich in harmonics so that by throwing the switches 34, 35 land 36 to positions alternate to thosev shown, the output of the oscillator 19 may be coupled to the input circuits of the amplifiers 3|, 32 and 33 so that they may amplify the eighth, sixth and ninth harmonics respectively of the reference oscillator output. The reference oscillator is preferably of a type which produces an output rich in the higher harmonics and in which the multiple phase relation between these harmonics is fixed -and unchanging. During final testing and adjustment following construction, the various circuit components are preferably adjusted to give `a zero lreading on the two phase indicators 10 and 11 when the reference oscillator 19 is connected to the amplifier inputs. Whenever at subsequnt times the switches 34-36 are turned to the alternate positions the phase indicators 10 and 11 should read zero and .any deviation from this standard reference reading constitutes an indication that some part of the apparatus requires adjustment.

The reference oscillator 19 is also made of the adjustable frequency type so that in the event the amplifier tuning is changed as described in the preceding paragraphs to other frequencies, such as 8.8, 66 and 99 kilocycles, the oscillator frequency may be similarly changed to 11 kilocycles to permit a check on the operation of the system to be made at the new frequency.

In the foregoing description, reference has been made to the reference oscillator 19 and the harmonic generator 41 as operating at a relatively low frequency fundamental and capable of producing an output rich in the higher harmonies. Any suitable oscillator or harmonic generator having these properties may be employed. However, I prefer to use a signal generator of the type disclosed in my copending application Serial No. 612,988, filed August 27, 1945, now Patent No. 2,524,677 and entitled Signal Generator.

Although, as previously stated, the phase discriminators 64 and 13 and the phase indicators 10 and 11 also may be of any suitable type, a preference is expressed for the types shown respectively in my Patent No. 2,500,200 above mentioned and in my Patent No. 2,499,326 issued February 28, 1950.

Attention-is directed to the fact that the tuning of the apparatus may be changed as vdesired to permit one group of navigational system transmitters to ybe selected out of a plurality of such groups which may be arranged as a chain or network of navigational systems to cover extremely large areas. It will be noted that the principal amplifying function of the receiving apparatus is done in the heterodyne frequency amplifiers, and that these amplifiers may be of the xed frequency type permitting high gain to be realised and permitting great phase stability to be readily obtained and easily maintained.

Attention is yalso directed to theV fact that the phase comparison is made at frequencies lower than the lowest frequency transmitted by the navigational system transmitters and that regardless of the frequency at which the phase comparison is made, the phase relation which is indicated by the phase indicators is that which corresponds to a phase measurement made at a frequency equal to the lowest common multiple of the unlikeyfrequencies whose multiple phase relation is to be determined.

While I have shown and described the preferred embodiment of my invention I do not desire to be limited to the details of construction shown and described herein, except as defined in the -appended claims.

I claim:

l. In a receiving apparatus for use with a, radio frequency navigational system operating to transmit from spaced points a pair of radio frequency signals of unlike but related frequencies 4bearing a fixed multiple phase relation to each other, the combination of z a pair of adjustable frequency radio frequency receivers tuneable respectively to the frequencies of said signals; a pair of adjustable radio frequency amplifiers tuneable to two other frequencies of a ratio equal to the ratio of the frequencies of said signals; an adjustable frequency source of alternating electrical potential of non-sinusoidal wave form tuneable to a frequency equal to a common factor of said two other frequencies; means for applying said potential to the input circuits of said amplifiers; means for combining and rectifying the outputs of each receiver and corre- Sponding amplifier to produce a pair of heterodyne signals of fixed frequency; a pair of frequency converters for producing from said heterodyne frequencies a pair of output signals of like frequency; and means for continuously determining and indicating the phase relation between said output signals.

2. In a receiving apparatus for use with a radio frequency navigational system operating to transmit from spaced points a pair of radio frequency signals of unlike but related frequencies bearing a fixed multiple phase relation to each other, the combination of a pair of adjustable frequency radio frequency receivers tuneable respectively to the frequencies of said signals; a pair of adjustable radio frequency regenerative amplifiers tuneable to two other frequencies of a ratio equal to the ratio of the frequencies of said signals; an adjustable frequency source of alternating electrical potential of non-sinusoidal wave form tuneable to a frequency equal to a common factor of said two other frequencies; means for applying said potential to the input circuits of said amplifiers; means for combining and rectifying the outputs of each receiver and corresponding amplifier to produce a pair of heterodyne signals of xed frequency; -a pair of 7. freq-uencyf` conyerters' for producing fcinr: said hetiodyne -freque'ncies aipair-i-` of output.' Isignals of like frequency;' and'imean's lfor 'continuously. determining and indicatingthe pha'se-relation' between saidloutput signals.'y

3. The rmethod .of determining thei'imultiple. phase rel'ationbetweenfafpairof-:radio frequency signals `of unlike but related "-frequeni'iies'f` which includes the stepsof heterodyning saidi .signals with local:v alternating potentials! of `different frequencies of-f a -ratio -equaL tu'` the -ratio 'of thefrequencies of isaid 'sign-als,` and measuring the multiple *phase relation: between` the resulting `het-- erodyne vfrequencies-by:generating a pair of reference Isignals-'of fknownl'm-ultiple" phasel relation and then Vmeasuring thelidifference betWeenL-th`e multiple phase relations'of said' heterodyne frequenciesfresulting fromsa-idreceived signals and resulting from" saidl generated t"signals,

4:= The method of 4determining the multiple phase 'relation' between' alpair of. radio vfrequency signals of unlike but related frequencies which consists inseparately-receivin'g said signals, heterodyning said signalswitli local alternating potentials' of different frequencies ofaratio equal to the "ratio of theL frequencies fof said Vvsignals, subjecting each 'of "the resulting heterodyne frequencies to frequency -mult-iplications selected to produce a pair of normal output signals'of a given equal frequency, measuring the phase relationbetween said normalv output signals by generati'n'g'a pair-ofreference 4signals of different 'frequencies of a ratio equal to the vratio of the frequenciesnof saidreceivedsignals and of k'nown multiple phase *relation* and.AV heterodyning said refrence'signals 'with said'loc'a'l alt'ernating'p'otentials and subjectingthefresulting heterodyne frequencies to frequency vmultiplications selected to produce a'pair of' standard output signals of s-aid Agiven equalI frequency; and then measuring therdiiference betweenithe phaserelations of said standard output 'signals an'd said'normaloutput signals, and continuously indicating the resultof" said measurement.

5. Ina receiving apparatus for use `with 'a radio frequency navigational' system operating to transmit from `spaced point-s apairof radio fre# quency signals of unlike butr related frequencies 'bearingfia f'iied Pmultiple phase :relationvto each other; the'fcombinationaof ar` pair of frequency radio frequency` receiversftuned respectively to thefrequ'encies of said` signals; a pair of radio frequency amplifiers tuned to two other frequencies of a ratio equal' to the ratio of the frequencies of said signals; a Isource of alternatingA electrical potential of non-sinusoidal wave form ofV a frequencyequal to a common factor of said twoother frequencies; means for applying said Vpotential to theinput circuits of said am# pliers; means for combining and rectifying the `outputsof each'Y receiver and corresponding ampliertoprodu'ce' a pair of heterodyne signals; a pair-.of frequency converters for producing from said heterodyne frequencies a pair of output signals'of like'frequency; and means for continuously determinin'gf'and indicating the phase relation' between said output signals.

6. Inan apparatus 'for determining the multiplerfph'a-se'relationV between a pair of radio frequencysignals of unlike 4but related frequencies, the combinationf'of:V a-source of two alternating electrical potentials of different frequencies of a ratio equal vto the ratio of the frequencies of said signals; heterodyningvmeans connected tov said source and having a pair 'of inputs to which said lsignals are 'applied' for heterodyning said potentials witli'the corresponding signals Ato produce a pair of normal output signals; means for substitutingfonsaid inputs apair of reference signais'` of knownmultiple phase relation for said radio f frequency signals lto thereby produce a pair-.f of f' substitute output signals; and means connected ftd saidheterodyning vmeans for comparing the multiple phase relation between said normal output "signals `Withthe multiple phase relation'betwee'nv said substitute output signals.

WILLIAM J. OBRIEN.

REFERENCES CITED vThe following references are of record in the file of this patent:

UNITED STATES PATENTS Numberv Name Date 1,447,204 Espenschied Mar. 6, 1923 1,939,434 Busse Dec. 12, 1933 

